1. Field of the Invention
The invention relates to a control apparatus for a fuel injection valve, which performs opening and closing operations on a fuel injection valve provided in an internal combustion engine (an engine), and a method thereof.
2. Description of Related Art
An energization period of a fuel injection valve during a single fuel injection is separated into an opening period for opening the injection valve and a holding period for holding the injection valve in an open condition. During the opening period, power is supplied to a solenoid of the fuel injection valve from a capacitor capable of applying a higher voltage than a battery. During the opening period, therefore, an excitation current flowing in the solenoid is increased. In this case, an electromagnetic force generated by the fuel injection valve grows gradually stronger until the injection valve opens. When the excitation current reaches a peak current value set as a current value at which the fuel injection valve opens reliably, the opening period ends and the holding period begins. During the holding period, power is supplied to the solenoid of the fuel injection valve from the battery. During the holding period, therefore, the excitation current decreases rapidly from the peak current value and is held in the vicinity of a holding current value. In this case, the electromagnetic force generated by the fuel injection valve is held at a force required to hold the fuel injection valve in the open condition.
During the opening period, the electromagnetic force increases gradually as the excitation current flowing in the solenoid increases, and therefore the fuel injection valve actually opens after the elapse of a certain amount of time following a point at which energization of the solenoid is started. A period from the energization start point to the opening point at which the fuel injection valve actually opens is referred to as an “injection standby period”. Further, a period from the energization start point to a point at which the fuel injection valve closes is referred to as an “effective injection period”.
The effective injection period becomes steadily shorter as a required injection amount set in relation to a single fuel injection decreases. The injection standby period, in contrast to the effective injection period, is a period determined in accordance with an operating characteristic of the fuel injection valve at that time, and unlike the effective injection period, does not therefore vary in proportion to the required injection amount. Hence, when the required injection amount set in relation to a single fuel injection is small such that the energization period is short, the injection standby period occupies a larger proportion of the energization period. Accordingly, an effect of an estimation error of the injection standby period increases as the energization period of a single fuel injection shortens, and as a result, an actual fuel injection amount is more likely to diverge from the required injection amount.
When the actual injection amount is larger than the required injection amount, torque adjustment can be performed by adjusting an ignition timing or the like in order to reduce the generated torque. When the actual injection amount is smaller than the required injection amount, however, it is difficult to increase the torque. It is therefore necessary to estimate the injection standby period accurately to ensure that the actual injection amount does not fall below the required injection amount.
Japanese Patent Application Publication No. 2012-97693 (JP 2012-97693 A) discloses an example of a method of learning variation in the injection standby period. More specifically, a current waveform is selected in accordance with the required injection amount and so on, and the fuel injection valve is controlled on the basis of the selected current waveform. When a condition for learning the variation in the injection standby period is established during a fuel injection, the variation in the injection standby period is learned using the current waveform selected to control the fuel injection valve as a parameter.
Note that the injection standby period may be estimated using a method of detecting an increase gradient of the excitation current on which the excitation current increases to the peak current value during the opening period, and setting the injection standby period to be steadily longer as the increase gradient becomes gentler.